Traditionally during the excavation of coal deposits, e.g. beds of bituminous coal, filling material is injected to reduce the settling of the roof (overlying beds) and rock structure. As such, the extent of damage due to mining and the reduction of the effects of pressure on mining installations is greatly reduced.
In addition the deployment of filling material is of importance to mine ventilation, the climate within the mine and the protection of the environment against the release of gases and the like.
Particularly in the German mining industry, filling operations have been unable to keep up with the exploitation of the mine and with standing support techniques over the last two decades. Similar problems have been encountered in other countries in which mining is significant. As a consequence, there have been considerable detrimental results, including damage to surface formations resulting from the mining, depth-related pressure and mine-climate conditions and the problems stemming from storage of mining debris.
Consequently, the stabilization of controlled collapsed regions in such mines has provided technical and economic advantages which have caused such approaches to become widespread.
However, the introduction or deployment of filling material does not find practical application in modern fully automated space mining operations unless there is a certain thickness of the coal bed, at this time approximately 1.8 meters. Where there is a deeply inclined coal bed, the use of conventional filling materials may not be able to stabilize the structure because the filling material, with the high angle of slope, itself is not easily stabilized.
The introduction of a pneumatic packing requires more costly labor and material support and presupposes a suitable infrastructure to enable the entire operation to be carried out and to provide the storage facilities and the facilities for handling the material which is to be injected.
Economic conditions have encouraged the increased use of controlled caving where the bringing down of the roof is carried out after the removal of the coal deposits. Because of the increase in volume of the loose debris, the resulting hollow spaces must be filled which, in turn, provides fresh support for the new main roof structure thus formed.
This problem cannot be solved by loose debris which is available from the collapse or with conventional packing of this debris and, as a consequence, the downward pressure of the strata lying above the collapsed region may be insufficiently supported.
In addition to the danger of environmental damage, the fact that hollow spaces of varying volume may result from the controlled caving, presents significant problems because gases are not easily eliminated. Ventilation of the mine becomes a problem and mine fires can result from spontaneous combustion.